Cutting insert

ABSTRACT

A cutting insert of the present invention has a body, auxiliary cutting edges of a convex curve shape and main cutting edges. The body has a top surface, a bottom surface, side surfaces connecting the top and bottom surfaces, and corner surfaces connecting the adjacent side surfaces. The auxiliary cutting edges are formed at intersections between the top and bottom surfaces and the side surfaces. The main cutting edges are formed at intersections between the top and bottom surfaces and the corner surfaces. The main cutting edge in the top surface extends from an end of an adjacent auxiliary cutting edge to its center in a direction toward the bottom surface and from the center to an end of another adjacent auxiliary cutting edge in a direction away from the bottom surface.

TECHNICAL FIELD

The present invention generally relates to a cutting insert for acutting tool, and more particularly to a cutting insert used for aprecision cutting process.

BACKGROUND ART

A cutting insert is firmly coupled to a body of a tool in order toprovide the tool with cutting edges. FIG. 1 shows a cutting insert fixedto a milling cutter using a screw. A cutting insert may also be coupledto the body of a tool by other means such as wedge fixing means.

FIGS. 2 to 6 show a conventional cutting insert and a milling cutterwith such a cutting insert mounted thereto.

FIG. 2 is a perspective view of a cutting insert, while FIG. 3 is a sideview thereof. The cutting insert 100 comprises a top surface 112, abottom surface 114 and four side surfaces 116 connecting the top surface112 and the bottom surface 114. The side surface 116 is connected to theother adjacent side surface 116 through a corner surface 118. Further, acurved auxiliary cutting edge 122 having a radius of curvature R isformed at the intersection between the top and bottom surfaces 112, 114and the side surface 116. A main cutting edge 124 is formed at theintersection between the top and bottom surfaces 112, 114 and the cornersurface 118. The main cutting edge 124 connects an auxiliary cuttingedge 122 to an adjacent auxiliary cutting edge 122. The top surface 112and the bottom surface 114 include a mounting surface 126 and a rakesurface 128. The rake surface 128 extends at an inclined angle “a” withrespect to the mounting surface 126.

FIG. 4 is a view taken from the corner surface 118 (i.e., in a directionindicated by A). As shown in FIG. 4, the main cutting edge 124 of theconventional cutting insert 100 extends horizontally.

FIG. 5 shows a state where a milling cutter with a conventional cuttinginsert mounted thereto cuts a surface of a workpiece. FIG. 6 is anenlarged view of a part B of FIG. 5. As shown in FIG. 5, the maincutting edge 124 of the cutting insert 100 performs the function ofinitially cutting a workpiece along the feed direction of the millingcutter, while the auxiliary cutting edge 122 performs a precisioncutting to smoothly polish the portion of the workpiece cut by the maincutting edge 124.

However, due to the manufacturing tolerance of the milling cutter andthe cutting insert 100, as well as the mounting error caused whenmounting the cutting insert 100 onto the milling cutter, differences inthe height of the cutting edges are generated. In order to make theprocessed surface flat with a high degree of precision, the influence ofthe error needs to be minimized. As such, the auxiliary cutting edge 122is formed in the shape of a convex curve having a curvature radius R,which ranges from 100 mm to 200 mm.

Further, the cutting performance of the main cutting edge 124 is closelyassociated with the axial rake angle of the main cutting edge 124. Theaxial rake angle represents an angle at which the main cutting edge 124is inclined relative to the rotation axis of the milling cutter. Asshown in FIG. 6, a relief angle is formed to avoid any surface contactbetween the side surface 116 of the cutting insert 100 and theworkpiece. Such an axial rake angle can have a positive value, 0 or anegative value. The positive value represents a case wherein the cuttinginsert is inclined opposite to the rotational direction of the millingcutter. The negative value represents a case wherein the cutting insertis inclined towards the rotational direction of the milling cutter. Thevalue of 0 represents a case wherein the cutting insert is not inclinedrelative to the rotational axis. When the axial rake angle has apositive value that becomes greater, chips are more easily eliminatedand the cutting resistance is reduced. However, in a conventionalcutting insert 100 as shown in FIG. 6, the axial rake angle of the maincutting edge 124 has a negative value (−5° in FIG. 6) to maintain arelief angle generally in the range of 4° to 6°.

Accordingly, since the cutting resistance is significant in the maincutting edge 124 portion, the cutting performance is poor, therebycausing other problems. In particular, when a depth of cut exceeds about0.5 mm, due to an increase in the cutting resistance, burrs are producedon the processed surface of the workpiece or the main cutting edge 124applies an excessive pressure to the processed surface of the workpiece,thereby deforming or breaking the structure. Because of these reasons,the depth of a cut is remarkably limited when the conventional cuttinginsert is used for a precision cutting, which requires a very smallsurface roughness.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve the foregoing problemsof the prior art, reduce cutting resistance against the main cuttingedge during the cutting process and improve the cutting performance bycreating a positive axial rake angle with the main cutting edge formedat the corner surface of the cutting insert. Particularly, the presentinvention is directed to providing a cutting insert that can performprecision cutting with a depth of cut greater than about 0.5 mm.

Furthermore, the object of the present invention is to provide a cuttinginsert that reduces the friction force on the workpiece during thecutting process by lowering the radius of curvature of the auxiliarycutting edge.

In order to achieve the above object, the present invention provides acutting insert, which comprises: a body of a rectangular parallelepipedshape, the body comprising a top surface, a bottom surface, a pluralityof side surfaces connecting the top and bottom surfaces, and a pluralityof corner surfaces connecting the adjacent side surfaces; one or moreauxiliary cutting edges of a convex curve shape, the auxiliary cuttingedges being formed at intersections between the top and bottom surfacesand one or more of the plurality of side surfaces; and one or more maincutting edges formed at intersections between the top and bottomsurfaces and one or more of the plurality of corner surfaces. Each ofthe top surface and the bottom surface comprises a mounting surface anda rake surface extending at an inclined angle with respect to themounting surface. The main cutting edge in the top surface extends froman end point of an adjacent auxiliary cutting edge to a center of themain cutting edge in a direction towards the bottom surface, and fromthe center to a meeting point with another adjacent auxiliary cuttingedge in a direction away from the bottom surface. The main cutting edgein the bottom surface extends from an end point of an adjacent auxiliarycutting edge to the center of the main cutting edge in a directiontowards the top surface, and from the center to a meeting point withanother adjacent auxiliary cutting edge in a direction away from the topsurface.

According to one embodiment of the present invention, the cutting inserthas 90° rotation symmetry about an axis passing through centers of thetop and bottom surfaces. It also has 180° rotation symmetry about anaxis passing through centers of the side surface and the opposite sidesurface thereof. A distance between a line extending from the auxiliarycutting edge to the center of the main cutting edge is 1.0 mm to 2.0 mmwhen seen from the top surface.

According to one embodiment of the present invention, the main cuttingedge in the top surface or the bottom surface makes an angle of 8° to18° with the mounting surface of the top surface or the bottom surfacewhen seen from the corner surface. The radius of curvature of theauxiliary cutting edge is 20 mm to 60 mm.

According to one embodiment of the present invention, the main cuttingedge comprises a straight part and curved parts located at both endsthereof when seen from the top surface. The straight part of the maincutting edge makes an angle of 45° with an adjacent auxiliary cuttingedge. The length of the auxiliary cutting edge is 40% to 60% of thedistance between the side surface and the opposite side surface thereofwhen seen from the top surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the milling cutter with a cutting insertmounted thereto.

FIG. 2 is a perspective view of a conventional cutting insert used for aprecision cutting process.

FIG. 3 is a side view of the cutting insert of FIG. 2.

FIG. 4 is a side view taken from the corner surface of the cuttinginsert of FIG. 2.

FIG. 5 is a view showing that a milling cutter with the cutting insertof FIG. 2 mounted thereto is in use.

FIG. 6 is an enlarged view of a part B of FIG. 5.

FIG. 7 is a perspective view of a cutting insert according to anembodiment of the present invention.

FIG. 8 is a side view of the cutting insert of FIG. 7.

FIG. 9 is a view showing a milling cutter with the cutting insert ofFIG. 7 mounted thereto is in use.

FIG. 10 is an enlarged view of a part D of FIG. 9.

FIG. 11 is a side view taken from the corner surface of the cuttinginsert of FIG. 7.

FIG. 12 is a view showing the cutting insert of FIG. 7 during thecutting of a workpiece.

FIG. 13 is a top view of the cutting insert of FIG. 7.

FIG. 14 is a top view of a cutting insert according to anotherembodiment of the present invention.

DETAILED DESCRIPTION

The present invention will now be described with reference toembodiments shown in the accompanying drawings.

FIG. 7 is a perspective view of a cutting insert according to oneembodiment of the present invention. FIG. 8 is a side view of thecutting insert of FIG. 7. The cutting insert 10 has a generallyrectangular parallelepiped shape. The cutting insert has top and bottomsurfaces 12, 14, which are opposite to and extend parallel to eachother, and four side surfaces 16 vertically connecting the top surface12 and the bottom surface 14. One side surface 16 is connected toanother adjacent side surface 16 through a corner surface 18. Thecutting insert 10 includes a mounting bore 20, through which a screwpasses to fix the cutting insert 10 to a body of a tool. As shown inFIG. 8, an intersection between the top surface 12 and the side surface16 (or the bottom surface 14 and the side surface 16) defines anauxiliary cutting edge 22 of a convex curve shape with a radius ofcurvature R. An intersection between the top surface 12 and the cornersurface 18 (or the bottom surface 14 and the corner surface 18) definesa main cutting edge 24. One auxiliary cutting edge 22 is connected toanother adjacent auxiliary cutting edge 22 through the main cutting edge24. Each of the top surface 12 and the bottom surface 14 is comprised ofa mounting surface 26 and a rake surface 28. The rake surface 28 isinclined from the auxiliary cutting edge 22 and the main cutting edge 24at an inclined angle “a” with respect to the mounting surface 26. Thecutting insert 10 has 90° rotation symmetry about an axis passingthrough the centers of the top surface 12 and the bottom surface 14.Further, the cutting insert has 180° rotation symmetry about an axispassing through the centers of the side surface 16 and the opposite sidesurface thereof.

FIG. 9 shows that a milling cutter with the cutting insert of FIG. 7mounted thereto performs a cutting process on a workpiece. FIG. 10 is anenlarged view of a part D of FIG. 9. As shown in FIG. 9, the maincutting edge 24 of the cutting insert 10 performs the function ofinitially cutting the workpiece along a feed direction of the millingcutter, while the auxiliary cutting edge 22 performs a precision cuttingto smoothly polish the portion of the workpiece, which is cut by themain cutting edge 24. Meanwhile, a cutting performance of the maincutting edge 24 is closely related to an axial rake angle of the maincutting edge 24. It is advantageous that the axial rake angle has apositive value so as to reduce a cutting resistance.

FIG. 11 is a view taken from the corner surface of the cutting insert ofFIG. 7 (i.e., in a direction indicated by C). The main cutting edge 24in the top surface 12 extends from an end point 32 of an adjacentauxiliary cutting edge 22 to a center 34 of the main cutting edge 24 ina direction towards the bottom surface 14, and extends from the center34 of the main cutting edge 24 to a meeting point with another adjacentauxiliary cutting edge 22 in a direction away from the bottom surface24. Similarly, the main cutting edge in the bottom surface 14 extendsfrom an end point of an adjacent auxiliary cutting edge to the center ofthe main cutting edge in a direction towards the top surface, andextends from the center of the main cutting edge to a meeting point withanother adjacent auxiliary cutting edge in a direction away from the topsurface. In other words, the main cutting edge 24 in the corner surface18 has the lowest height at the center 34 when seen from the cornersurface 18.

The main cutting edge 24 in the top surface 12 or the bottom surface 14makes an angle “b” of 8° to 18° with the mounting surface of the topsurface 12 or the bottom surface 14 when seen from the corner surface(i.e., in the direction indicated by C). The cutting insert 10 ismounted to the milling cutter with a relief angle therebetween in orderto avoid any surface contact to the workpiece. Preferably, the angle “b”is equal to or greater than 8° such that the axial rake angle of themain cutting edge 24 of the cutting insert 10 has a positive value evenwith such a relief angle. In contrast, too much of a large angle “b” notonly makes it difficult to fabricate the cutting insert but alsodecreases the stiffness of the cutting insert. Thus, it is preferablethat the angle “b” is equal to or less than 18°. Since the main cuttingedge 24 is formed as described above, the axial rake angle of the maincutting edge 24 of the cutting insert 10 according to the presentinvention is allowed to have a positive value (e.g., +13° in FIG. 10)when the cutting insert 10 is mounted to the milling cutter and cuts aprocessed surface of the workpiece as shown in FIG. 10. Accordingly, thecutting resistance in the main cutting edge 24 portion is reduced andthe cutting performance is remarkably improved when compared to aconventional cutting insert.

FIG. 12 shows that the cutting insert of the present invention cuts theworkpiece. The cutting insert 10 performs a cutting process while oneauxiliary cutting edge 22 and one main cutting edge 24 are contacted tothe workpiece. For example, in the state shown in FIG. 12, the auxiliarycutting edge 23 and the main cutting edge 25 perform the cuttingprocess. More specifically, since the cutting insert 10 is mounted astilted towards the main cutting edge 25 contacted to the workpiece, themain cutting edge 25 and a right side of the auxiliary cutting edge 23mainly perform the cutting process. However, the cutting process may beperformed by the auxiliary cutting edge 23 (mainly, a left side of theauxiliary cutting edge) and the main cutting edge 25′ by reversing arotational direction of the cutting insert. Further, the cutting processmay be performed by the auxiliary cutting edge 23′ and the main cuttingedge 25″ or 25′″ by altering the mounting position of the cuttinginsert. Since the cutting insert 10 has 90° rotation symmetry about theaxis passing through the centers of the top surface 12 and the bottomsurface 14 and 180° rotation symmetry about the axis passing through thecenters of the side surface 16 and the opposite side surface thereof asdescribed above, the cutting insert includes four auxiliary cuttingedges 22 and four main cutting edges 24 at each of the top surface 12and the bottom surface 14. The main cutting edges 24 are bilaterallysymmetrical about the center 34 as shown in FIG. 11. Thus, the cuttinginsert 10 has sixteen identically shaped pairs of an auxiliary cuttingedge and a main cutting edge (e.g., 23 and 25, 23 and 25′) in total(more specifically, eight pairs at the top surface 12 and eight pairs atthe bottom surface 14). Accordingly, a single cutting insert 10 may beused sixteen times, thereby providing an economical use.

FIG. 13 is a top view of the cutting insert of FIG. 7. FIG. 14 is a topview of a cutting insert according to another embodiment of the presentinvention. As shown in FIGS. 13 and 14, a distance “c” between a lineextending from the auxiliary cutting edge 22 to the center of the maincutting edge 24 is about 1.0 mm to 2.0 mm when seen from the topsurface. Thus, when the cutting insert 10 performs the cutting processas mounted to a body of a tool, even in case a depth of cut exceeds 0.5mm and reaches about 1.0 mm, the axial rake angle of the main cuttingedge 24, which is formed at the corner surface 18 of the cutting insert10, has a positive value with respect to such depth of cut. Thus, aproblem caused by increase of the cutting resistance does not occur evenin the case of the depth of cut of about 1.0 mm. Further, problems thatburrs are produced on the processed surface of the workpiece and thatthe main cutting edge 24 applies excessive pressure to the processedsurface of the workpiece to deform or break its structure areeliminated. Accordingly, the cutting insert of the present invention canincrease a depth of cut which can perform a precise cutting process whencompared to the conventional cutting insert.

Further, the main cutting edge 24 of the cutting insert shown in FIG. 13is comprised of a straight part 38 and curved parts 40 located at bothends thereof when seen from the top surface. The main cutting edge 24 isbilaterally symmetrical about the center 34. The straight part makes anangle of 45° with the adjacent auxiliary cutting edge 22. The cornersurface 18 is comprised of a flat surface and curved surfaces located atboth sides thereof. The flat surface makes an angle of 45° with theadjacent side surface 16. Further, the main cutting edge 24 of thecutting insert shown in FIG. 14 is comprised of only a curved part(indicated by R4.27 in FIG. 14) and the corner surface 18 is comprisedof only a curved surface. The auxiliary cutting edge 22 performs aprecision cutting to smoothly polish the portion of the workpiece cut bythe main cutting edge 24. A shorter auxiliary cutting edge limits a feedamount of the workpiece and slows down a processing speed. Accordingly,as for cutting inserts having the same depth of cut, the main cuttingedge 24 comprised of the straight part and the curved parts located atboth ends thereof has an advantage of having a longer auxiliary cuttingedge 22 than the main cutting edge 24 comprised of only the curved part.

Specifically, when the cutting inserts shown in FIGS. 13 and 14 are seenfrom the top surface, the distances “c” between the line extending fromthe auxiliary cutting edge 22 to the center 34 of the main cutting edge24 are the same. However, in the case shown in FIG. 13 where the maincutting edge 24 is comprised of the straight part 38 and the curvedparts 40 located at both ends thereof, the length of the auxiliarycutting edge 22 is about 40% to 60% of the distance between the sidesurface and the opposite side surface thereof (e.g., 6.04 mm in FIG.13). In the case shown in FIG. 14 where the main cutting edge 24 iscomprised of only a curved part, the length of the auxiliary cuttingedge 22 is about 30% to 50% of the distance between the side surface andthe opposite side surface (e.g., 4.16 mm in FIG. 14).

As shown in FIG. 8, the auxiliary cutting edge 22 of the cutting insert10 of the present invention has a convexly curved shape wherein itsmiddle portion is upward or downward higher than both sides thereof whenseen from the side surface. Preferably, its radius of curvature R is ina range of 20 mm to 60 mm. As such, the cutting insert 10 of the presentinvention has the auxiliary cutting edge 22 with a small radius ofcurvature. Thus, a friction force on the workpiece, which is generatedduring cutting process, becomes small.

Thus, as seen in the side view of FIG. 8, each auxiliary cutting edge 22has a convexly curved shape and a distance between centers of opposingauxiliary cutting edges associated with the top surface 12 and bottomsurface 14 defines a maximum height for the viewed side surface 16 andadjacent corner surfaces 18. Meanwhile, as seen in the FIG. 11 cornerview of the cutting insert, the main cutting edge 14 has a concaveshape, a distance between centers 34 of main cutting edges 24 associatedwith the top surface 12 and the bottom surface 14 defines a minimumheight for the viewed corner surface 18 and adjacent side surfaces 16.

While the present invention has been described by way of preferredembodiments thereof, those embodiments are for exemplary purposes only.It will be understood by those of ordinary skill in the art that variousalternations or modifications may be made without departing from thescope of the present invention. The cutting insert according to oneembodiment of the present invention includes a mounting bore and isfixed to a body of a tool by means of a screw passing through themounting bore. However, it may not include the mounting bore and may befixed by means of other fixing means such as a wedge fixing means, whichis obvious to those of ordinary skill in the art. The cutting insertaccording to one embodiment of the present invention has a generallyrectangular parallelepiped shape. The cutting edges are formed at all ofthe intersections between the top or bottom surface and the side orcorner surfaces. However, it is obvious to those of ordinary skill inthe art that the cutting edges are formed only at some of theintersections. Such alternations or modifications obvious to those ofordinary skill in the art fall within the scope of the presentinvention.

As described above in detail, the present invention provides a cuttinginsert which reduces cutting resistance against the main cutting edgeduring the cutting process and improves the cutting performance bycreating a positive axial rake angle with the main cutting edge formedat the corner surface of the cutting insert.

1. A cutting insert, comprising: a body including a top surface, abottom surface, a plurality of side surfaces connecting the top surfaceand the bottom surface, the body further including a plurality of cornersurfaces connecting adjacent side surfaces; one or more auxiliarycutting edges with a convex curve shape, the auxiliary cutting edgesbeing formed at intersections between the top and bottom surfaces andone or more of the plurality of side surfaces; and one or more maincutting edges formed at intersections between the top and bottomsurfaces and one or more of the plurality of corner surfaces, whereineach of the top surface and the bottom surface comprises a mountingsurface and a rake surface extending at an inclined angle with respectto the mounting surface; wherein the main cutting edge in the topsurface extends from an end point of an adjacent auxiliary cutting edgeto a center of the main cutting edge in a direction towards the bottomsurface, and from the center to a meeting point with another adjacentauxiliary cutting edge in a direction away from the bottom surface; andwherein the main cutting edge in the bottom surface extends from an endpoint of an adjacent auxiliary cutting edge to the center of the maincutting edge in a direction towards the top surface, and from the centerto a meeting point with another adjacent auxiliary cutting edge in adirection away from the top surface.
 2. The cutting insert according toclaim 1, wherein the cutting insert has 90° rotation symmetry about anaxis passing through centers of the top and bottom surfaces; and whereinthe cutting insert has 180° rotation symmetry about an axis passingthrough centers of side surfaces on opposite sides of the cuttinginsert.
 3. The cutting insert according to claim 1, wherein a distancebetween a line extending from the auxiliary cutting edge to the centerof the main cutting edge is 1.0 mm to 2.0 mm, in a top view of thecutting insert.
 4. The cutting insert according to claim 1 wherein, in acorner view of the cutting insert: the main cutting edge in the topsurface makes an angle of 8° to 18° with the mounting surface of the topsurface; and the main cutting edge in the bottom surface makes an angleof 8° to 18° with the mounting surface of the bottom surface.
 5. Thecutting insert according to claim 1, wherein a radius of curvature ofthe auxiliary cutting edge is 20 mm to 60 mm.
 6. The cutting insertaccording to claim 1, wherein, in a top view of the cutting insert, themain cutting edge comprises a straight part and curved parts located oneither side of the straight part.
 7. The cutting insert according toclaim 6, wherein the straight part of the main cutting edge forms anangle of 45° with an adjacent auxiliary cutting edge.
 8. The cuttinginsert according to claim 6, wherein, in a top view of the cuttinginsert, the length of the auxiliary cutting edge is 40% to 60% of thedistance separating side surfaces on opposite sides of the cuttinginsert.
 9. The cutting insert according to claim 1, wherein, in a topview of the cutting insert, the main cutting edge comprises only acurved part which connects two adjacent auxiliary cutting edges.
 10. Thecutting insert according to claim 1, wherein the cutting insert has arectangular parallelepiped shape.
 11. The cutting insert according toclaim 10, wherein, in a top view of the cutting insert, the auxiliarycutting edges all have the same length.
 12. A cutting insert,comprising: a body including a top surface, a bottom surface, four sidesurfaces connecting the top surface and the bottom surface, and fourcorner surfaces connecting adjacent side surfaces; auxiliary cuttingedges formed at intersections between the top and bottom surfaces, andthe side surfaces; main cutting edges formed at intersections betweenthe top and bottom surfaces, and the corner surfaces, each main cuttingedge connecting adjacent auxiliary cutting edges; a mounting surfaceassociated with each of the top and bottom surfaces; and a rake surfaceassociated with each mounting surface and extending at an inclined anglewith respect to said each mounting surface; wherein: in a side view ofthe cutting insert, each auxiliary cutting edge has a convex curve shapeand a distance between centers of auxiliary cutting edges associatedwith the top and bottom surfaces defines a maximum height for the viewedside surface and adjacent corner surfaces; and in a corner view of thecutting insert, each main cutting edge has a concave shape and adistance between centers of main cutting edges associated with the topand bottom surfaces defines a minimum height for the viewed cornersurface and adjacent side surfaces.
 13. The cutting insert according toclaim 12, wherein: in a side view of the cutting insert, a distancebetween the mounting surfaces defines a maximum height of the cuttinginsert.
 14. A cutting insert, comprising: a body including a topsurface, a bottom surface, four side surfaces connecting the top surfaceand the bottom surface, and four corner surfaces connecting adjacentside surfaces; auxiliary cutting edges formed at intersections betweenthe top and bottom surfaces, and the side surfaces; and main cuttingedges formed at intersections between the top and bottom surfaces, andthe corner surfaces, each main cutting edge connecting adjacentauxiliary cutting edges; wherein: in a side view of the cutting insert,each auxiliary cutting edge has a convex curve shape and a distancebetween centers of auxiliary cutting edges associated with the top andbottom surfaces defines a maximum height for the viewed side surface andadjacent corner surfaces; in a corner view of the cutting insert, eachmain cutting edge has a concave shape and a distance between centers ofmain cutting edges associated with the top and bottom surfaces defines aminimum height for the viewed corner surface and adjacent side surfaces;and in a top view of the cutting insert, the main cutting edge comprisesa straight part and curved parts located on either side of the straightpart.
 15. The cutting insert according to claim 14, wherein the straightpart of the main cutting edge forms an angle of 45° with an adjacentauxiliary cutting edge.
 16. The cutting insert according to claim 14,wherein, in a top view of the cutting insert, the length of theauxiliary cutting edge is 40% to 60% of the distance separating sidesurfaces on opposite sides of the cutting insert.
 17. The cutting insertaccording to claim 12, wherein, in a top view of the cutting insert, themain cutting edge comprises only a curved part which connects twoadjacent auxiliary cutting edges.
 18. The cutting insert according toclaim 12 wherein the cutting insert has a rectangular parallelepipedshape.
 19. The cutting insert according to claim 18, wherein, in a topview of the cutting insert, the auxiliary cutting edges all have thesame length.
 20. The cutting insert according to claim 14, wherein: thecutting insert has a rectangular parallelepiped shape; and in the topview of the cutting insert, the auxiliary cutting edges all have thesame length.